Basic methods for processing agricultural products using heat are generally known. Agricultural-product processing, for instance making pelleted feed for livestock, can typically include grinding raw material, storing material, mixing ration additives to create mash, steam conditioning, pelletizing, and pellet cooling and drying. It is sometimes desirable to dry and cool pellets output from this system to within about six degrees Celsius (about ten degrees Fahrenheit) of ambient-air temperature in order to control product moisture in storage bins, and thus prevent growth of mold.
Before entering a pellet mill, mash has generally been steam conditioned by injecting, for example, five points of steam into the mash. One point of steam means adding an amount of steam equal to one percent of the weight of the product mash being heated. Steam conditioning is also useful in the agricultural-production process in that it may sterilize the agricultural product, cook the product to make nutrients more available, and/or gelatinize starch in the product so the product is better capable of sticking together.
Climate changes affect the output from an agricultural-product processor. Industry trends have shown that, when ambient air temperatures are higher, production is increased and the production process is more cost efficient. The raw material and ambient air, used in the process, are already at a higher temperature when input into the system, thereby cutting down on energy costs because the product requires less additional heat than is necessary when raw material and ambient air temperatures are cooler, such as in winter months.
Similar processes involving grinding raw material, steam conditioning/heating, cooling and drying are also used in ethanol production, wet corn milling, sugar production, wood-pellet production (e.g., pellets for burning in home wood-pellet-burning stoves to generate residential heat), and other processing of agricultural products. These processes typically include at least some of the above functions, in particular steam moisturizing and conditioning/heating.
In U.S. Pat. No. 4,659,299 (incorporated herein by reference), a system is described in which “pre-heated mash is pelleted to thereby form warm pellets. Thereafter, the warm pellets are cooled by ambient air and the ambient air is heated by the heat from the warm pellets. The heated ambient air is used to pre heat the mash.” “The airflow path is provided from the ambient air inlets through the dryer/cooler, through the belt conveyor to cool and remove moisture from the warm pellets and pick up heat, through the conveyor to pre-heat the mash and then exits the air dryer/cooler through the warm air conduit. The belt conveyor conveys the mash through the warm air in the air flow path to pre-heat the mash.”
This U.S. Pat. No. 4,659,299 starts to address energy use and efficiency problems, but the belt conveyer mechanism used in this invention for cooling the pellets does not address inefficiencies related to a co-flow system or cross-flow system or an uneven dispersion of pellets. Because U.S. Pat. No. 4,659,299 describes a single cross-flow system using inefficient heat transfer (typically, a belt or tray requires high air flow and is prone to channeling, wherein most of the air goes through the spots with fewest pellets and least resistance), the system is typically unable to cool the agricultural product to a temperature below that of the intermediate moist exhaust air. The exhaust air is typically unable to reach a temperature higher than that of the pellet output. The dispersion of pellets created by the belt conveyor in this patent leaves the problem of an uneven spread of pellets. If the pellets are not spread uniformly in the cooling process, the air used to cool the product will travel through the path of least resistance, or where the fewest number of pellets are located. This will cause an inconsistent and inefficient cooling and drying of the pellets, and a lower quality product output. The belt-conveyor cooler is now usually considered obsolete technology that is generally being replaced in the industry by more efficient counterflow devices.
U.S. Pat. No. 4,929,163 (incorporated herein by reference) describes a system “which utilizes moisture in its liquid phase, i.e., water, and heat in the form of hot air, but no steam in converting the dry material into a mash suitable for pelleting.” This is done for purposes of “separating the temperature input from moisture input such that they may be individually adjusted independently of each other,” thereby purportedly addressing the problems of using steam in which “an increase in the amount of steam increases both moisture and temperature and vice versa.”
U.S. Pat. No. 4,935,874 (incorporated herein by reference) describes a system to control a vapor steam generator by sensing exhaust temperature of the steam. U.S. Pat. No. 4,935,874 proposes controlling mash temperature and moisture at the pellet mill using a plurality of temperature sensors. It does not account for variances in temperature or moisture content of the incoming “dry” material and the effect these have on the moisture at the pellet mill. Further, it describes a vapor steam generator similar to that shown in U.S. Pat. No. 4,211,071 (incorporated herein by reference) operating “at a constant pressure of between 4-6 psi” and proposes a “control mode for the vapor steam generator which permits it to generate a continuous flow of steam at a preselected moisture content, and yet provide temperature control of the steam produced”. This “mode of control comprises modulating the flow of the air/gas mixture to the burner while maintaining a relatively constant water flow”. An air/gas mixture is electronically controlled to deliver the appropriate flow of the air/gas mixture to the combustion chamber. Water input is independently controlled and introduced into the combustion chamber where a burner burns the air/gas mixture and converts the water directly into steam. A temperature sensor downstream from the combustion chamber senses the temperature of steam (i.e., the steam before it enters a stirring conditioner to warm and moisturize the mash), in order to control the flow of the air/gas mixture to maintain a constant temperature of the steam produced. The moisture content of the steam can be controlled by controlling the rate of water input into the combustion chamber. To try to produce finished pellets having a pre-determined moisture content, U.S. Pat. No. 4,935,874 describes controlling the rate of input of dry material as well as the rate of input of water into the combustion chamber. Its conditioner has dry material entering the top, being stirred as the material flows downward and as the vapor and air flow upward though the material, proportioning the amount of moisture to the rate of flow of dry material. It utilizes the operation of the burner to control the temperature of the exhaust steam while maintaining a rate of flow of moisture as desired to suit the flow of dry material into the pellet mill. The temperature of the steam and the moisture input to the combustion chamber are not independent. For any set flow or the air/gas mixture the temperature of the steam will be controlled by the water input. As the water input increases the temperature of the steam will decrease, as the water input decreases the temperature of the steam will increase. Further, for any set rate of water input, increasing the flow of the air/gas mixture will increase the temperature of the steam, while any decrease in the flow of the air/gas mixture will decrease the temperature of the steam. Independent control of temperature, moisture and flow are not provided.
As described by C. B. Theurer et al. in Invited Review: Summary of Steam-Flaking Corn or Sorghum Grain for Lactating Dairy Cows, Journal of Dairy Science Vol. 82, No. 9, 1999: The net energy for lactation of steam-flaked corn or sorghum grain is about 20% greater than the net energy for lactation for dry-rolled corn or sorghum. Steam-flaking of corn or sorghum grain with careful quality control consistently improves most lactational measurements, especially milk and milk protein yields.
Theurer et al. further describe that steam-rolling is a common processing method for barley, corn, and wheat used in dairy concentrates. Grains are usually steamed for 15 minutes or less to increase grain moisture to about 15 percent and then crushed with various sizes of rollers to produce a thick flake without a specific flake density endpoint, usually about 438 to 540 g/L for corn and sorghum (34 to 42 lb./bu., in units as used in the industry). Quality is usually based on visual appraisal rather than steaming time, moisture content, flake density, or laboratory indices. Dry-rolling is a common form of processing barley, sorghum, and wheat; dry grain is passed through large rollers (46 to 76 cm or larger) to break the grain into several pieces (similar to coarsely ground), with a bulk density for sorghum of about 450 to 644 g/L (35 to 50 lb/bu).
Theurer et al. still further describe that steam flaking is a more extensive processing system (with careful quality control) than dry- or steam-rolling. In some embodiments, whole grain is steamed for 30 to 60 minutes in a vertical, stainless steel steam chamber (usually 3.1 to 9.2 m height and 91 to 183 cm diameter) to increase grain moisture to 18 to 20% and then flaked between preheated large rollers (e.g., 46 cm diameter by 76 to 91 cm length or 61 cm diameter by 122 cm length) to a specific desired flake density (usually 309 to 386 g/L or 24 to 30 lb/bu) (53). In most cited studies, the grain was steam flaked to a flake density (FD) of about 360 g/L and is referred to as SF 28 (reflecting the flake density in pounds per bushel after steam flaking). The rollers become hot as the steamed grain passes through, which is important in the flaking process. The extent of processing (flaking pressure) increases as flake density decreases (i.e., 309 g/L flake is more extensively processed than a 386 g/L flake). The quality of steam-flaked grain is routinely measured by flake density, and by laboratory methods (enzymatic starch hydrolysis or percent starch gelatinization).
U.S. Pat. No. 6,330,982 (incorporated herein by reference) describes a grinding system that allows for processing of both coarse and fine particles.
U.S. Pat. No. 5,486,102 (incorporated herein by reference) describes a pellet mill.
U.S. Pat. No. 4,674,418, (incorporated herein by reference) describes a cyclone cleaner.
What is needed is a system and method for processing an agricultural-product with improved heat and moisture recovery and control.